Modify dateutil.f
Modify dateutil.f

1. Compartmentalize code more, separating command
   line options, checking for inputs, and computing
   dates into separate subroutines.
2. Add option to use different formats for inputs.
3. Add option for long format input/output with
   hours, minutes, and seconds.
4. Add subroutine rdarg to parse input format.
5. Add option to input date/days on command line
   instead of through files.
6. Update usage subroutine to reflect changes.

mherman09/Hdef,mherman09/Hdef,mherman09/Hdef